In a defect inspection for a substrate with a pattern, the sensitivity of defect detection is largely affected depending on how a detected light beam from defects can be detected while being distinguished from a detected light beam (background light noise) from a pattern or a base film. Especially, with advanced fine patterning, detection of finer defects is required in an inspection for a semiconductor wafer, and extracting a weak detected light beam from fine defects while being distinguished from background light noise is a major challenge in an inspection technique.
Here, a vertical structure of a substrate with a pattern as an inspection target and the types of defects to be detected will be described in FIG. 2 using a semiconductor wafer as an example.
In FIG. 2, a vertical structure of a semiconductor device will be described using the reference numerals 20 to 35 and 201 to 251, and defects as inspection targets will be described using the reference numerals 261 to 264.
The reference numeral 20 denotes an element separating layer with a structure (202) in which after digging grooves in a silicon (Si) substrate 201, oxide silicon (SiO2) as an insulating material is embedded to electrically insulate and separate a transistor element formed on a wafer. The reference numerals 21 and 211 denote a gate and contact layer and a gate electrode portion made of polysilicon (poly-Si), respectively. This area largely affects the performance of the transistor, and is important in an inspection. The reference numeral 212 denotes a contact portion formed in such a manner that metal (tungsten: W and the like) is embedded into a hole formed on an insulating film (oxide silicon: SO2) by etching to connect the transistor portion to an upper wiring layer. The reference numerals 22 to 25 denote wiring layers by which circuits are formed. Each layer is embedded with an insulating film (oxide silicon: SiO2 and the like). The reference numeral 22 denotes a first wiring portion in which a first wiring portion 221 is used to be wired in a planar direction and a first via portion 222 is a portion formed in such a manner that metal is embedded into a hole formed on an insulating film (oxide silicon: SiO2 and the like) by etching to be connected to a further-upper wiring layer. Likewise, the reference numeral 23 denotes a second wiring layer in which the reference numerals 231 and 232 denote a second wiring portion and a second via portion, respectively. The reference numeral 24 denotes a third wiring layer in which the reference numerals 241 and 242 denote a third wiring portion and a third via portion, respectively. The reference numeral 25 denotes a fourth wiring layer in which the reference numeral 251 denotes a fourth wiring layer. In each wiring layer, material of the wiring portions is made of metal such as aluminum (Al) or copper (Cu). Further, the metal embedded into the via portions is made of tungsten (W) or copper (Cu).
In addition, defects as inspection targets include scratches 261, short-circuits 262 and disconnections 263 as pattern defects, and foreign particles 264.
FIG. 3 are explanatory diagrams of processes, materials, and typical defects in the respective layers of the semiconductor device shown in FIG. 2. The respective layers of the semiconductor device are formed by a material deposition process for forming each layer, resist pattern formation by a lithography process, an etching process to remove and process the deposited material in accordance with the formed resist pattern, and a CMP (Chemical Mechanical Polishing) process for flattening.
For example, as an apparatus for optically inspecting a semiconductor wafer formed through the respective processes, Patent Literature 1 discloses a technique related to a semiconductor wafer defect inspection apparatus having an illumination system of white light sources in addition to an illumination system of laser light sources.
Further, as a high-coherent broadband light source used for an illumination light source, there is a supercontinuum light source that generates broadband supercontinuum light (SC light) by allowing long and short pulse laser beams to enter a photonic crystal fiber (PCF) in which holes are periodically arranged in the cross-section of the optical fiber as disclosed in Non-patent Literature 1, or an optical frequency comb generator in which electrooptic crystal provided in a resonator is modulated with microwaves by an external transmitter and a single-wavelength laser beam is allowed to enter there to generate light beams with broadband and multi-wavelength spectrums at modulation frequency intervals of microwaves centered on the input single-wavelength laser beam as disclosed in Non-patent Literature 2. Further, as an example of a two-dimensional microshutter array that can be used for a spatial filter of an apparatus for optical inspection, Non-patent Literature 3 and Non-patent Literature 4 disclose a configuration in which thousands to tens of thousands of minute optical shutters having a size to of one to a few hundred of micrometers are arranged and integrated in the X-Y directions using an MEMS (Micro Electro Mechanical Systems) technique, so that each shutter can be individually controlled to be opened or closed.